user
Write a function to find the longest word in a sentence.
assistant

def find_longest_word(str): 
  words = str.split() 
  longest_word = ""
  longest_length = 0
  for word in words: 
    word_length = len(word) 
    if word_length > longest_length:
      longest_length = word_length
      longest_word = word 
 
  return longest_word